This invention relates to hot melt coating compositions, in particular, to stabilized compositions of a cellulosic and an oil extender.
Due to their physical properties such as coating capability, strength, thermal stability and ease of removal; hot melt compositions of ethyl cellulose and an oil extender are widely used as temporary protective coatings for various articles such as tools, machinery and the like.
In a typical operation, a coating formulator prepares the hot melt compositions by mixing an ethyl cellulose, an oil extender (generally a mineral oil) and other adjuncts, e.g., plasticizers and heat stabilizers, with constant agitation and heat until a solution occurs. The resulting solution is solidified by cooling to ambient temperatures, i.e., 20.degree.-30.degree. C. During this solidification, the mixture is formed into blocks or other convenient shapes for shipment and subsequent storage.
In the coating operation, the solid blocks of the hot melt composition are reheated to a molten form, with temperatures from 125.degree. to 190.degree. C. conventionally being employed. The part to be coated is dipped in the molten composition for a short period, e.g., 1-5 seconds, then withdrawn and excess material drained therefrom. The composition solidifies on the part upon cooling, forming the temporary protective coating.
Unfortunately, the oil extender in the composition often tends to exude excessively from the composition in its solidified form. Such oil exudation causes handling and packaging problems and creates a fire and safety hazard in storage facilities. Moreover, the exuded oil is not generally recoverable, thereby necessitating the replacement of the lost material. In addition, the compatibility of the hot melt components, i.e., ethyl cellulose, oil extender and other adjuncts, is often poor in the solidified composition, as evidenced by the crazing, swirling and the like therein.
Heretofore, oil exudation has been decreased by reducing the concentration of the oil in the hot melt composition. See, for example, U.S. Pat. Nos. 2,517,754 and 2,951,763. Unfortunately, such practice is economically undesirable.
In view of these stated deficiencies, it is highly desirable to furnish a hot melt coating composition containing a cellulosic and substantial amounts of an oil extender which composition exhibits reduced oil exudation and improved compatibility.